1. Field of the Invention
The present invention relates to an antenna apparatus and a wireless communication apparatus, and more particularly is suitably applied to a cellular phone capable of using two types of wireless communication systems, for example, different in used wireless communication frequency.
2. Description of the Related Art
In recent years, cellular phones have a tendency to become insufficient in the number of lines only for a single wireless communication system with a rapid spread.
Accordingly, in cellular phones, it is considered that two types of wireless communication systems using different frequency bands are jointly used to ensure the required number of lines and there has been developed a terminal capable of using two types of wireless communication systems by,means of a single cellular phone.
Actual complex terminals include such as, in Japan a complex terminal jointly using two wireless communication systems of a Personal Digital Cellular (PDC) using an 800 MHz band and a Personal Handyphone Systems (PHS) using a 1.9 GHz band of wireless communication frequencies, in Europe a complex terminal jointly using two wireless communication systems of a Global System for Mobile Communication (GSM) using a 900 MHz band and a Digital Communication System (DCS) using a 1.8 GHz band, and in the United States of America a complex terminal jointly using two wireless communication systems of an Advanced Mobile Phone Service (AMPS) using an 800 MHz band and a Personal Communications Services (PCS) using a 1.9 GHz band.
And, among such cellular phones, there are those provided with two antenna apparatuses operating at first and second wireless communication frequencies different from each other and those provided with a single antenna apparatus having two types of first and second antenna elements integrated into one piece.
Here, in an antenna apparatus having first and second elements integrated into one piece, the first antenna element 1 and the second antenna element 2 are integrated by the electrical connection to an antenna feeding part 3 via a common feeding point as shown in FIG. 1.
In this antenna apparatus, the electrical length extending from an antenna feeding part 3 to the open end of the first antenna element 1 is chosen to the order of xcex/4 of one of a first wireless communication frequency out of two types of first and second wireless communication frequencies and that extending from the antenna feeding part 3 to the other open end of the second antenna element 2 is chosen to the order of xcex/4 of the other of the second wireless communication frequency lower than the first one, for example.
Thus, the first antenna element 1 resonates at the relevant first wireless communication frequency during the use of the first wireless communication frequency and the first antenna element 1 alone operates as the antenna because an excess of electrical length for resonance of the second antenna element 2 at the first wireless communication frequency prevents the second antenna element 2 from resonating.
Besides, the second antenna element 2 resonates at the relevant second wireless communication frequency during the use of the second wireless communication frequency and the second antenna element 2 alone operates as the antenna because a shortage of electrical length for resonance of the first antenna element 1 at the second wireless communication frequency prevents the first antenna element 1 from resonating.
Such being the case, a cellular phone provided with such an antenna apparatus selectively uses first and second antenna elements corresponding to the first wireless communication frequency and the second wireless communication frequency used and therefore two different types of wireless communication systems are so arranged as to be jointly employed.
Meanwhile, in recent years, the absorption factor of an electromagnetic wave per time and per mass at a specific region (chiefly head) of a human body has been defined as the local average Specific Absorption Rate (SAR) and it has been required to suppress a maximum of the local average SARs below a prescribed value among electromagnetic waves irradiated from the cellular phone.
Here, in a cellular phone, the electric power fed from the antenna feeding part to the antenna element serving for the chief irradiation source of electromagnetic waves differs depending on wireless communication frequency used in general and the electric field of electromagnetic waves irradiated from the antenna element becomes more intense with increasing electric power.
And, if an antenna element irradiating electromagnetic waves of a relatively strong electric field and another irradiating electromagnetic waves of a relatively weak electric field are respectively disposed the same distance apart from a human body, the disposition of the antenna element irradiating electromagnetic waves of a relatively strong electric field shows a tendency for the local average SAR to rise.
Furthermore, a distance between the antenna element and the human body is disposed to become shorten in accordance with a tendency of recent miniaturization light weight in the cellular phone, and thinness, and consequently, the more the antenna element approaches the human body, the more the local average Specific Absorption Rate (SAR) increases.
In the antenna apparatus mentioned above in FIG. 1, the first and second antenna elements 1 and 2 are glued to the outer periphery of an antenna casing (unillustrated) made of a cylindrical nonconductive material, the antenna casing is simply inserted in the casing case of the cellular phone (unillustrated) and no measure for suppressing the local average SAR is taken.
In view of the foregoing, an object of this invention is to provide an antenna apparatus and a wireless communication apparatus capable of reducing the absorption factor of electromagnetic waves absorbed by a human body during the telephone call even when at least two or more antenna elements are disposed.
The foregoing object and other objects of the invention have been achieved by the provision of an antenna apparatus and a wireless communication apparatus in which an antenna element indicating the higher absorption factor was disposed by antenna disposing means the more distant from a human body on the basis of the absorption factor of electromagnetic waves absorbed by the human body, measured in advance when at least two or more antenna elements different in electrical length operate respectively as antennas under the same disposing conditions.
Consequently, even if at least two or more antenna elements are disposed, the absorption factor of electromagnetic waves absorbed by a human body during the telephone call can be reduced in such a degree as to keep an antenna element indicating the higher absorption factor the more distant from the human body.
Besides, antenna hold means is so arranged as to collectively hold all individual antenna elements electrically connected to a common feeding point, at this time such positioning is made by antenna positioning means that antenna elements are arranged in the decreasing order of absorption factor and the installation posture of the antenna hold means is so regulated by the posture regulation means that an antenna element indicating the higher absorption factor is kept the most distant from a human body when installing the antenna hold means to the installation means.
Thus, all individual antenna elements can be so disposed that an antenna element indicating the higher absorption factor is securely kept the more distant from a human body.
The nature, principle and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings in which like parts are designated by like reference numerals or characters.